Method of uniformly heating metal pieces



1966 CHUNG LAo FENG 3 9 METHOD OF UNIFORMLY HEATING METAL PIECES Filed Nov. 6, 1962 INVENTOR CHUNG LIAO FENG ATTORNEY.

United States Patent O 3,234,055 METHOD OF UNIFORMLY HEATING METAL PIECES Chung Liao Feng, Horsham, Pa., assignor to Selas Corporation of America, Dresher, Pa., a corporation of Pennsylvaria Filed Nov. 6, 1962, Ser. No. 235,751

i 3 Claims. (Cl. 148-13.1)

The present invention relates to a method of heating metal, and more particularly to a method of uniformly and rapidly heating metals having different surface conditions or a low surface emissivity.

In the heating of various metals, suoh as aluminum and brass for example, difliculty is encountered in bringing various pieces to the same temperature within the same time. T his is due in large part to the varying emissivity of the surface of the pieces to be heated. Small pieces or slugs of aluminum or brass are prepared for hot working, such as forging, and stored until such time as they are needed. During the storage period the surface condition of the various slugs will alter appreciably, some being quite tamished and others bright. When placed in a furnace to be heated, those slugs with tarnished surfaces will heat faster, or to a higher temperature in a given time, than those having bright surfaces. This is due to the different surface emissivity of the diiferent pieces. The result is that it is difficult, if not impossible, to heat slugs of this type to an optimum forging temperature on a production line basis.

It is an object of the invention to coat uniformly the surfaces of a plurality of slugs as they a-re moving through a furnace so that t hey will be heated uniformly.

It is a further object of the invention to darken the surface of a bright metal object so that it willabsorb heat more rapidly than would otherwise be the case.

In practicing the invention, slugs are moved one after the other through a furnace chamber having such a temperature and atmosphere that carbon is deposited uniformly over the surface of the slugs. "Dhe so-coated slugs then having a uniform surface appearance are moved into a heating zone of the furnace to be brought up to temperature. Since each slug then presents a similar surface to the furnace, they will be heated to substantially the same' temperature in the same time. In addition, the dark coating of the carbon increases the speed of heating of slugs that were bright when moved into the furnace. The carbon coating disappears when the heated slug is removed from the furnace.

The various features of novelty which characterize my invention are pointed out with particula-rity in the claims annexed to and forming a part of this specification. For a better Understanding of the invention, however, its advantages and specific -objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have llustrated and described a preferred embodiment of the invention.

In the drawings: FIG. 1 is a view, in section, of one type of furnace that may be used to carry out the invention, and

FIG. 2 is a section taken on line 2--2 of FIG. 1.

Referring to the drawings, there is shown a furnace 1 having a floor 2 and end walls 3 and 4. The furnace is divided by a partition 5 into a pair of chambers 6 and 7. The end walls and t-he partition are provided with openings 8 that are shaped to conform with and closely encircle the work pieces as they are moved through the furnace on an endless conveyor belt 9. This belt passes over and is driven by pulleys 11 and 12, and is provided along its length with a plurality of sockets 13 into which the work pieces, shown herein by way of example only 3,234,055 Patented Feb. 8, 1966 as cylindrical slugs, 14 are received. The slugs can be placed on the sockets either manually or automatically and fall from the sockets down a discharge chute 15 to a work station, such as a forge, as the belt passes around pulley 12.

The chambers 6 and 7 are heated by burners 16 which may be of any conventional type, either flame or radiant, to the desired temperature. Fuel supplied to the burners is regulated by valves 17 which may be controlled manually or automatically in any conventional manner. The bottom or floor of chamber 6 is provided with a pair of openings through which the branches of a pipe 18 extend. This pipe is used to supply raw gas to the chamber with the supply being regulated by a valve 19. The gas is supplied through the floor so that it Will be closer to the portion of the chamber through which the pieces to be heated are moved.

In carrying out the method, the first furnace chamber 6 is heated by burners 16 to a temperature at least equal to that at which the fuel gas being used will onack. If the gas is natural gas, for example, the temperature of chamber 6 will be at least 1S00F. The fuel supply to burners 16 is preferably stoichiometric, and in any event the products of combustion will be substantially neutral. G as is introduced into the bottom of chamber 6 through pipe 18. This gas is regulated by valve 19 until the atmosphere in the chamber has at least an equivalence ratio of 1.88 for the gas being used. With such conditions the excess gas will crack so that free carbon is produced in the furnace chamber.

The slugs, or other work pieces to be heated, are placed manually or automatically on fixtures 13 and moved at a constant speed through the furnace, The pieces being heated are normally at ambient temperature, or in any event less than 300 F., as they move into the furnace. Because of their relatively cool temperature, the free carbon in the furnace chamber will immediately start to preci pitate or be deposited in an even coating over the entire exposed surface of the piece, and each piece will be completely coated by the time the piece reaches F. Belt 9 is moved at such a speed with relation to the length of chamber 6 that the pieces will reach at least this temperature -before they enter chamber 7. The carbon forms a uniform, thin, dark coating on each piece regardless of its original surface condition or color. Thus, the emissivity of the surface of each piece is substantially the same and for bright pieces is increased.

chamber 7 is heated to a temperature dependent upon the final temperature of the work, but will ordinarily be in the neighborhood of 2400 F. At this temperature the walls of the chamber will be ncandescent so that a large percentage of the heating of the pieces will be by radiant heat, with the remainder being by convection from the burner gases. The absorption of radiant heat depends upon the emissivity of the surface of the piece being heated. A piece having a bright surface or one of low emissivity requires a longer time to be heated to a given temperature than a piece with a dull surface. Since each of the pieces has been coated so that -it presents the same dull surface to the furnace, each piece Will be heated substantially to the same temperature by the time it reaches the exit of the furnace. In addition, those pieces that Originally had a bright surface will be heated faster than otherwise would have been the case.

The speed of the conveyor is such that the pieces will be brought up to hot working or some other desired temperature by the time they fall from the holders 13 on discharge chute 15. For aluninum the hot Working ternperature will be in the neighborhood of 1000 F. and for brass in the neighborhood of 1500 F.

As soon as the hot pieces are contacted by the atmosphere, if they are heated to between 1000 F. and 1200 F., the carbon coating will disappear, apparently burned off, leaving the piece with its original surface. In` those cases where the piece is heated to above 1200 F, the

coating will burn off at about that temperature. By that time, however, an oxide will be formed on the surface so that the heating rate will not be substantially afiected.

When the pieces are heated below 1000 F., as will be the rejects due to improper heating. The method may also be used for the continuous heating of strip metal; In such case the heating time of a bright strip such as aluminum, brass or stainless steel is reduced, andthe strip is evenly heated even though it may have dark streaks or Spots on it.

While in accordance with the provisions of the statutes, I have illustrated and described thebest form of embodimentvof my invention now known to me, it willbe appare-nt to those skilled in the .art that changes may be' Such heating increases the efficency of a ing individual treatment given to the various pieces and i made in the form of the apparatus disclosed without de-. y

partingf from the spirit and scope of the invention set i tures of my tinvention may be usedto advantage' without forth in the appended claims, and that in some 'cases certain features of my invention may be used to advantage without a corresponding use of other features.

What is claimed is:

1. The method of heating uniformly to' hot working temperature metal pieces having varyirg surface conditions which comprises:

moving said pieces one after the other at a constant i speed through a furnace having two adjoining chambers,

heating the first chamber through which the pieces travel to a temperature above which fuel gas will crack,

introducing fuel gas into said first chamber to crack the depositing a layer of carbon from the cracked gas on the surfaces' of said pieces as they move through said first chamber, 3

heating the second chamber through whichgthe pieces travel to a temperature suicient to bring said pieces up to the desired hot Working temperature by the time` they leave said chamber,.and

heating the earbon covered pieces in said second chamber to hotworking temperature by; radiation and convect'on heat whereby'each piece, regardless of its original surface condition, Will be heated to substantially the same temperature in'substantially the same time as they leave said second chamber.

2. The method of heating metal pieces to hot working temperature which comprises moving the pieces through a furnace at a constant rate, creating in a first portion of the furnace ,through which the pieces pass a fuel gas rich atmosphere at a temperature suflicient to crack the gas, depositing carbon from the cracked gas evenly' over the surface of thezpieces in the first portion of the furnace, creating in the next portion of the furnace. a temperature sufficient to heat the -coated pieces to hot `working temperature, and heating each of :the pieces to substantially the same hot working temperature regardless of its original surface condition as it leaves the chamber.

3. The method of uniformly heating metal pieces having various surface characteristics which comprises moving said pieces one after the other througha path at, a uniforrn speed, surrounding a first portion of said path with an atmosphere containing free fuel gas at a temperature sufiicient to crack the gas, precipitating carbon from the cracked gason the surface of the' metal pieces to coat them uniformly with carbon, surrounding a second portion of said path with a temperature sufficient to *heat said pieces to hot working temperature and heating said uniformly coated pieces in` said second portion to sub stantially the same final desired temperature by the time they'leave said second portion.

References, Cited by the Examiner UNITED! STATES PATENTS 1,280,825 10/1918 Pacy 148-20.3 2,051,828 8/1936 Dester 148-203 X 2,865,797 12/ 1958 McCaWley 148-203 2,923,539 2/1960 Meyer -5 X DAVID L. RECK, Primary Exam'ne'. 

3. THE METHOD OF UNIFORMLY HEATING METAL PIECES HAVING VARIOUS SURFACE CHARCTERISTICS WHICH COMPRISES MOVING SAID PIECES ONE AFTER THE OTHER THROUGH A PATH AT A UNIFORM SPEED, SURROUNDING A FIRST PORTIO OF SAID PATH WITH AN ATMOSPHERE CONTAINING FREE FUEL GAS AT A TEMPERATURE SUFFCIENT TO CRACK THE GAS, PRECIIATING CARBON FROM THE CRACKED GAS ON THE SURFACE OF THE METAL PIECES TO COAT THEM UNIFORMLY WITH CARBON, SURROUNDING A SECOND PORTION OF SAID PATH WITH A TEMPERATURE SIFFCIENT TO HEAT SAID PIECES TO HOT WORKING TEMPERATURE AND HEATING SAID UNIFORMLY COATED PIECES IN SAID SECOND PORTION TO SUBSTANTIALLY THE SAME FINAL DESIRED TEMPEATURE BY THE TIME THEY LEAVE SAID SECOND PORTION. 